Corticotropin-releasing hormone (CRH, also called CRF or corticoliberin) was first characterized as a 41-residue peptide isolated from ovine hypothalami by Vale et al. (1981). Subsequently, the sequence of human-CRH was deduced from cDNA studies and shown to be identical to that of rat-CRH. Caprine, bovine, porcine, and white sucker fish CRH have also been characterized. The sequences of CRH from hoofed animals are considerably different from the human sequence, but the pig and fish sequences differ from the human/rat sequence by only 2 out of 41 residues.
Peptides with sequences homologous to that of mammalian CRH are found in cells of certain frog skins and in the urophysis of fish. The sequence of sauvagine, a 40-amino acid peptide isolated from the skins of Phyllomedusa frogs, was reported several years before Vale's description of ovine-CRH. The structure of sucker fish urotensin I was reported just months after the description of ovine-CRH and resulted from an independent line of inquiry by Lederis's group in Canada. Although sauvagine and urotensin I are known to induce release of adrenocorticotropin (ACTH) from the pituitary, the primary function of these peptides remains unknown.
In humans, CRH regulates, via release of proopiomelanocortin, ACTH secretion from the anterior pituitary and has several direct actions on central and peripheral tissues. CRH has also been found to have direct anti-inflammatory properties. More recently, evidence has been provided that mammalian skin cells both produce CRH and express functional CRH receptors (Slominski et al., FEBS Lett., 374, pp. 113-116, 1995; Slominski et al., J. Clin. Endocrinol. Metab., 83, pp. 1020-1024, 1998; Slominski et al., Hum. Pathol., 30, pp. 208-215, 1999), although it was not known whether locally produced CRH had an additional role in the physiology of the skin other than as a vasodilator and inhibitor of thermal injury-induced edema.
Some therapeutic methods and uses for CRH are described by Wei et al. in U.S. Pat. No. 4,801,612, issued Jan. 31, 1989, entitled “Method of Inhibiting Inflammatory Response,” and U.S. Pat. No. 5,137,871, issued Apr. 26, 1994, entitled “Treatment to Reduce Edema for Brain and Musculature Injury.” These patents describe the use of CRH to decrease the leakage of blood components into tissues produced by various adverse medical conditions, and thus to treat a patient for injury to or disease of the brain, central nervous system or musculature in which edema is a factor.
U.S. Pat. No. 5,869,450, issued Feb. 9, 1999, to Wei et al., describes CRH analogs in which the fifth amino acid from the N-terminus is D-Pro or in the case of urocortin or sauvagine where the fourth amino acid from the N-terminus is D-Pro or D-Ser. These analogs have an anti-inflammatory activity and a disassociated ACTH response.
Cyclic CRH agonists have been described by Rivier et al. (U.S. Pat. Nos. 5,844,074 and 5,824,771). These CRH analogs, modified by cyclization of residues 30-33 of CRH via a glutamic acid-lysine bridge, are more potent than native CRH in the release of ACTH and have lower molecular weights than native CRH. The elimination of residues 1-3 at the N-terminus of CRH has been shown to not alter biological activities or ACTH-release potency. (Kornreich et al., J. Med. Chem., 35, pp. 1870-1876, 1992; Koerber et al., J. Med. Chem., 41(25), pp. 5002-5011, 1998.)
Tjuvajev et al. in In Vivo, 12, pp.1-10, 1998 reported a series of in vivo and in vitro studies evaluating the anti-neoplastic potential of CRH in W256 rat mammary carcinoma. Using magnetic resonance imaging (MRI) and direct measurements of tumor and peritumoral brain water content they found that CRH treatment (100 micrograms/kg subcutaneously twice a day for 3 days) caused significant inhibition of growth of intracerebrally-injected W256 tumor cells. CRH also exhibited antiproliferative effects in in vitro cultures of W256 cells. The antiproliferative effects of CRH in W256 cells are believed to involve activation of nitric oxide synthase (NOS) and L-arginine-NO pathways.
In U.S. Pat. No. 6,319,900, Wei and Slominski disclose that CRH and members of the CRH superfamily, in which the 20th amino acid is replaced with a D-amino acid, have anti-proliferative activity.
Human trials of CRH for the treatment of peritumoral brain edema have been initiated and preliminary data indicate that CRH reduces brain edema associated with tumor metastases. However, the limiting factor on the use of CRH has been the known blood-pressure lowering property of CRH. CRH causes relaxation of smooth muscles surrounding blood vessels (vasodilation) resulting in a lowering of blood-pressure. The resultant hypotension is sufficiently dangerous to limit the dosages of CRH that can be administered to humans. Overcoming this dose-limiting toxicity by design of CRH superfamily peptide analogs that have less blood-pressure lowering activity should improve the therapeutic index and provide useful anti-proliferative therapeutics.